My DS is 13mo and I gained similar to you. I didn't start to lose weight until I went back to work when he was 5 mo away from the bloody fridge and could easily have done it much sooner by not grazing as much. I am still bf night and morning, and was pumping most other feeds up till recently. I'm now back at my pre-pregnancy weight. I reckon that three healthy meals a day, minimal snacking and plenty of water is the way to go. Your body will prioritise lactation. I was definitely consoling myself for sleep deprivation with snacks.

KellyMom has some stuff on this. The evidence looks a bit mixed but the advice seems to be don't actively try to lose weight until 8 weeks and thereafter don't try and go below 1,500-1800 calories a day as a minimum/don't try to lose too much too quickly (stick to half a kg a week).

Having said that- DS2 is 16 weeks. I gained 15kg in pregnancy and was a bit overweight to start with so I have a total of 15kg to lose. Started actively trying to lose weight 2 weeks ago just calorie counting and exercising more (--and cutting out the cake)-- and have lost 2.5kg so far. Obviously more than KellyMom suggests and I wasn't trying to lose weight that quickly, but that's what has happened and supply seems fine.

KellyMom suggestion is 3 small meals plus some snacks btw. Basically don't expect your body to have the same ability to have big gaps between meals when BF, so make meals smaller and plan to have healthy snacks.